120 research outputs found
The willow microbiome is influenced by soil petroleum-hydrocarbon concentration with plant compartment-specific effects
International audienceThe interaction between plants and microorganisms, which is the driving force behind the decontamination of petroleum hydrocarbon (PHC) contamination in phytoremediation technology, is poorly understood. Here, we aimed at characterizing the variations between plant compartments in the microbiome of two willow cultivars growing in contaminated soils. A field experiment was set-up at a former petrochemical plant in Canada and after two growing seasons, bulk soil, rhizosphere soil, roots, and stems samples of two willow cultivars (Salix purpurea cv. FishCreek, and Salix miyabeana cv. SX67) growing at three PHC contamination concentrations were taken. DNA was extracted and bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS) regions were amplified and sequenced using an Ion Torrent Personal Genome Machine (PGM). Following multivariate statistical analyses, the level of PHC-contamination appeared as the primary factor influencing the willow microbiome with compartment-specific effects, with significant differences between the responses of bacterial, and fungal communities. Increasing PHC contamination levels resulted in shifts in the microbiome composition, favoring putative hydrocarbon degraders, and microorganisms previously reported as associated with plant health. These shifts were less drastic in the rhizosphere, root, and stem tissues as compared to bulk soil, probably because the willows provided a more controlled environment, and thus, protected microbial communities against increasing contamination levels. Insights from this study will help to devise optimal plant microbiomes for increasing the efficiency of phytoremediation technology
Ătude thĂ©orique et numĂ©rique de systĂšmes thermophotoniques en champ proche appliquĂ©s Ă la rĂ©cupĂ©ration d'Ă©nergie
With 70% of the worldâs primary energy consumption being lost as heat during conversion, finding ways to make use of this waste heat is a key challenge. One way is to convert it back into useful energy with heat engines, for instance by using solid-state heat engines to directly convert heat into electricity. In this context, the field of near-field thermophotonics has recently attracted increasing interest. In such an engine, a light-emitting diode heated by the waste heat is placed in the immediate vicinity of a photovoltaic cell at room temperature. The radiation emitted by the light-emitting diode, which displays high intensity due to both electroluminescence and near-field effects, allows the photovoltaic cell to generate a significant amount of electrical power even for low heat source temperatures. Although the light-emitting diode consumes some of this electrical power to run, the complete device is still capable of generating substantial electrical power as long as the two components are efficient enough. In this thesis, we analyse the operation of near-field thermophotonic engines by theoretical and numerical means. To deepen the understanding of thermophotonic devices, the radiation-electricity conversion occurring in the light-emitting diode and the photovoltaic cell are first modelled using detailed-balance approaches. This allows developing an analytical upper limit for the efficiency at maximum power for both monochromatic and broadband radiation. We study the influence of several key quantities, and pinpoint the importance of achieving a high quantum efficiency for the device to reach high power output and efficiency. In a second step, the charge transport in semiconductors is simulated thanks to an in-house one-dimensional drift-diffusion solver including thermionic emission and charge carrier tunnelling at interfaces, enabling the investigation of complete structures. The first system considered is composed of AlGaAs and GaAs homostructures, and is found to be capable of generating a maximum power output of the order of 1 W.cmâ2 for an LED heated at 600 K. By analysing the charge transport in the two components, we highlight the importance of operating in the near field, the increase in quantum efficiency it causes being essential to achieve satisfactory operation. Because accounting for a significant surface recombination rate or including temperature and composition dependencies in the non-radiative recombination coefficients would make this device inoperable, we propose a new architecture based on heterostructures composed of InGaP confinement layers and InGaAs active layers. This allows reducing non-radiative losses and thus mitigates the power drop when the previously mentioned phenomena are included, with a reduction factor of 4 only. While several idealising assumptions still remains, this shall open a path for the design and optimisation of near-field thermophotonic engines.Dans un systĂšme thermophotonique en champ proche, une diode Ă©lectroluminescente chaude est placĂ©e Ă faible distance dâune cellule photovoltaĂŻque maintenue Ă tempĂ©rature ambiante. Le rayonnement Ă©mis par la diode Ă©lectroluminescente, qui prĂ©sente une intensitĂ© Ă©levĂ©e grĂące aux phĂ©nomĂšnes dâĂ©lectroluminescence et dâeffet tunnel de photons, permet Ă la cellule photovoltaĂŻque de produire une quantitĂ© importante dâĂ©nergie Ă©lectrique : le systĂšme convertit la chaleur fournie au corps chaud en Ă©lectricitĂ©. Dans cette thĂšse, on analyse le fonctionnement de ce systĂšme par des approches thĂ©oriques et numĂ©riques. La conversion rayonnement-puissance Ă©lectrique ayant lieu dans les deux composants est dâabord modĂ©lisĂ©e Ă lâaide dâĂ©quations de conservation. Cela permet de dĂ©velopper une expression analytique de la valeur maximale de lâefficacitĂ© au maximum de puissance pour un rayonnement monochromatique ou Ă large spectre. Des efficacitĂ©s quantiques Ă©levĂ©es doivent ĂȘtre considĂ©rĂ©es pour rendre la puissance de sortie et lâefficacitĂ© compĂ©titives. Le transport de charges dans les semi-conducteurs est ensuite simulĂ© grĂące Ă un code rĂ©solvant les Ă©quations de dĂ©rive-diffusion en une dimension et incluant lâĂ©mission thermoĂŻonique et lâeffet tunnel aux interfaces, permettant lâĂ©tude de structures rĂ©alistes. Lâoptimisation de systĂšmes composĂ©s dâhomostructures permet dâintroduire un dispositif capable de gĂ©nĂ©rer une puissance maximale de lâordre du W.cmâ2 pour une diode Ă©lectroluminescente Ă 600 K. Son analyse rĂ©vĂšle lâimportance de la conïŹguration en champ proche, lâaugmentation de lâefficacitĂ© quantique quâelle induit Ă©tant essentiel au bon fonctionnement du systĂšme. On propose ïŹnalement un dispositif plus robuste, basĂ© sur des hĂ©tĂ©rostructures composĂ©es de couches actives en InGaAs et de couches de conïŹnement en InGaP. Cette architecture permet de conserver une puissance Ă©lectrique Ă©levĂ©e mĂȘme lorsque des pertes auparavant nĂ©gligĂ©es sont considĂ©rĂ©es, la puissance maximale ne diminuant alors que dâun facteur 4. Ces travaux dĂ©montrent que cette technologie de rĂ©cupĂ©ration dâĂ©nergie originale est prometteuse pour des tempĂ©ratures de quelques centaines de degrĂ©s Celsius
Near-field thermophotonics: a numerical study of AlGaAs-GaAs devices
International audienc
Des centres et des marges. La trajectoire de Julie Doucet
Cet article propose dâanalyser la trajectoire de Julie Doucet en tant que rĂ©vĂ©latrice des dynamiques et enjeux relatifs aux sphĂšres de production culturelle dans lesquelles elle sâinscrit. Depuis ses dĂ©buts dans la bande dessinĂ©e « underground » montrĂ©alaise dans la deuxiĂšme moitiĂ© des annĂ©es 1980 jusquâĂ son prĂ©tendu « adieu » au mĂ©dia Ă la fin de la dĂ©cennie suivante, Julie Doucet a parcouru quelques-uns des lieux les plus importants de la bande dessinĂ©e nord-amĂ©ricaine et europĂ©enne. De MontrĂ©al Ă Berlin, en passant par New York, Portland (Oregon) et Paris, suivre cette trajectoire Ă©quivaut Ă cartographier le renouveau de la bande dessinĂ©e au cours de la dĂ©cennie 1990, des deux cĂŽtĂ©s de lâAtlantique. Lâoeuvre de Doucet a Ă©tĂ© largement Ă©tudiĂ©e et est considĂ©rĂ©e comme emblĂ©matique de la bande dessinĂ©e des annĂ©es 1990, car elle Ă©pouse quelques-unes des caractĂ©ristiques principales de lâĂ©poque : dimension autobiographique; travail sur le corps, la sexualitĂ© et lâabject; et un penchant fĂ©ministe. Ă ces thĂ©matiques, nous proposons dâajouter celle de lâĂ©clatement du mĂ©dia quâelle opĂšre par des formes et techniques nouvelles. Ă cet effet, une attention particuliĂšre sera dâailleurs accordĂ©e Ă la place quâoccupe la bande dessinĂ©e de Doucet dans un ensemble plus grand de pratiques, notamment la relation quâelle entretient avec les marges de la production culturelle. La production de zines de Doucet - tant avant sa professionnalisation au tournant des annĂ©es 1980 et 1990 quâaprĂšs son retrait au tournant 1990-2000 - en est le signe le plus Ă©vident. Il sâagit dâailleurs dâune question qui travaillera notre article de maniĂšre souterraine : comment se nĂ©gocie le rapport de la marge au centre pour une artiste comme Doucet, particuliĂšrement au regard de lâintĂ©gration tardive de la bande dessinĂ©e au champ culturel? De ce point de vue, un opĂ©rateur central de travail de Doucet se rĂ©vĂšle : le jeu avec le positionnement dâoutsider. Cet opĂ©rateur est perceptible Ă la fois Ă la lecture interne des oeuvres (le choix des thĂšmes, de la langue, et lâexploration formelle au coeur de sa dĂ©marche), et dans les choix Ă©ditoriaux et stratĂ©giques de lâautrice (le rapport Ă la bande dessinĂ©e sur la longue durĂ©e et le retour au zine, la mobilitĂ©, les commentaires de Doucet sur son parcours et son oeuvre). Cet article prĂ©sente finalement, et pour la premiĂšre fois, une bibliographie exhaustive des publications de Doucet, incluant toute sa production autoĂ©ditĂ©e, de la deuxiĂšme moitiĂ© des annĂ©es 1980 Ă aujourdâhui.This article studies Julie Doucetâs trajectory as a revelation of the dynamics and issues related to the spheres of cultural production in which the artist is embedded. From her beginnings in the Montreal âundergroundâ comic scene in the second half of the 1980s to her so-called âfarewellâ to the medium at the end of the following decade, Julie Doucet has journeyed through some of the most important venues in the world of North American and European comics, from Montreal to Berlin, via New York, Portland (Oregon) and Paris. Doucetâs work has been widely studied and is considered to embrace some of the characteristics of 1990s comics: body representation, sexuality and the abject; and a feminist inclination. To these themes, we propose adding the fragmentation of the medium in which she operates brought about by new forms and techniques. Particular attention will be given to the place that Doucetâs comics occupy in a larger set of practices, notably the close relationship that she maintains with the margins of cultural production. The relationship is most obvious in the production of Doucetâs zines - both before her professionalization at the turn of the 1980s and 1990s and since her withdrawal at the turn of 1990-2000. Our article addresses, in a somewhat subversive manner, the following question: how is the relationship between the margin and the center negotiated for an artist like Doucet, particularly in light of the late integration of comics into the cultural field? Examining Doucetâs work from such an angle reveals a central operator: her play with the outsider position. This operator is perceptible both in the internal reading of the works (the choice of themes and of language, and the formal exploration at the heart of her approach), and in Doucetâs editorial and strategic choices (the relationship to comics over the long term and the return to the zine, her mobility, her personal comments on her career and her work). Finally, our article presents an exhaustive ground-breaking bibliography of Doucetâs publications, including all of her self-published works, from the second half of the 1980s to the present
Near-field thermophonics: a numerical study of AlGaAs-GaAs devices
International audienc
On the method of reflections
International audienceThis paper aims at reviewing and analysing the method of reflections. The latter is an iterative procedure designed to linear boundary value problems set in multiply connected domains. Being based on a decomposition of the domain boundary, this method is particularly well-suited to numerical solvers relying on integral representation formulas. For the parallel and sequential forms of the method appearing in the literature, we propose a general abstract formulation in a given Hilbert setting and interpret the procedure in terms of subspace corrections. We then prove the unconditional convergence of the sequential form and propose a modification of the parallel one that makes it unconditionally converging. An alternative proof of convergence is provided in a case which does not fit into the previous framework. We finally present some numerical tests
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